Desertification

U.S. Department of Agriculture map from 1998 showing global desertification vulnerabilityLake Chad in a 2001 satellite image, with the actual lake in blue. The lake lost more than 90% of its surface area between 1987 and 2005.

Desertification is a type of land degradation in drylands in which biological productivity is lost due to natural processes or induced by human activities whereby fertile areas become increasingly more arid.[2] It is the spread of arid areas caused by a variety of factors, such as through climate change (particularly the current global warming)[3] and through the overexploitation of soil through human activity.[4]

When deserts appear automatically over the natural course of a planet's life cycle, then it can be called a natural phenomenon; however, when deserts emerge due to the rampant and unchecked depletion of nutrients in soil that are essential for it to remain arable, then a virtual "soil death" can be spoken of,[5] which traces its cause back to human overexploitation. Desertification is a significant global ecological and environmental problem with far reaching consequences on socio-economic and political conditions.[6]

Definitions of words

As recently as 2005, considerable controversy existed over the proper definition of the term "desertification." Helmut Geist (2005) identified more than 100 formal definitions. The most widely accepted[7] of these was that of the Princeton University Dictionary which defined it as "the process of fertile land transforming into desert typically as a result of deforestation, drought or improper/inappropriate agriculture".However, this original understanding that desertification involved the physical expansion of deserts has been rejected as the concept has evolved.[8] Desertification has been neatly defined in the text of the United Nations Convention to Combat Desertification (UNCCD) as "land degradation in arid, semi-arid and dry sub-humid regions resulting from various factors, including climatic variations and human activities."[9]

Another major contribution to the controversy comes from the sub-grouping of types of desertification, spanning from the very vague yet shortsighted view as the "man-made-desert" to the broader yet less focused type as the "non-pattern-desert".[10]

History

The world's most noted deserts have been formed by natural processes interacting over long intervals of time. During most of these times, deserts have grown and shrunk independent of human activities. Paleodeserts are large sand seas now inactive because they are stabilized by vegetation, some extending beyond the present margins of core deserts, such as the Sahara, the largest hot desert.[11]

Historical evidence shows that the serious and extensive land deterioration occurring several centuries ago in arid regions had three epicenters: the Mediterranean, the Mesopotamian Valley, and the Loess Plateau of China, where population was dense.[12][13]

The earliest known discussion of the topic arose soon after the French colonization of West Africa, when the Comité d'Etudes commissioned a study on desséchement progressif to explore the prehistoric expansion of the Sahara Desert.[14]

Areas affected

Drylands occupy approximately 40–41% of Earth's land area[16][17] and are home to more than 2 billion people.[17] It has been estimated that some 10–20% of drylands are already degraded, the total area affected by desertification being between 6 and 12 million square kilometres, that about 1–6% of the inhabitants of drylands live in desertified areas, and that a billion people are under threat from further desertification.[18][19]

As of 1998, the then-current degree of southward expansion of the Sahara was not well known, due to a lack of recent, measurable expansion of the desert into the Sahel at the time.[20]

The impact of global warming and human activities are presented in the Sahel. In this area the level of desertification is very high compared to other areas in the world. All areas situated in the eastern part of Africa (i.e. in the Sahel region) are characterized by a dry climate, hot temperatures, and low rainfall (300–750mm rainfall per year). So, droughts are the rule in the Sahel region.[21] Some studies have shown that Africa has lost approximately 650,000km² of its productive agricultural land over the past 50 years. The propagation of desertification in this area is considerable.[22]

Some statistics have shown that since 1900 the Sahara has expanded by 250km to the south over a stretch of land from west to east 6,000km long.[23][24][25] The survey, done by the Research Institute for Development, had demonstrated that this means dryness is spreading fast in the Sahelian countries. 70% of the arid area has deteriorated and water resources have disappeared, leading to soil degradation. The loss of topsoil means that plants cannot take root firmly and can be uprooted by torrential water or strong winds.[22][26]

The United Nations Convention (UNC) says that about six million Sahelian citizens would have to give up the desertified zones of sub-Saharan Africa for North Africa and Europe between 1997 and 2020.[22][26]

Lake Chad, located in the Sahel region, has been hit particularly hard by this phenomenon. The cause of the lake drying up is due to irrigation withdrawal and the annual rainfall dropping.[27] The lake has shrunk by over 90% since the 1987, displacing millions of inhabitants. Recent efforts have managed to make some progress toward its restoration, but it is still considered to be at risk of disappearing entirely.[28][1]

Another major area that is being impacted by desertification is the Gobi Desert. Currently, the Gobi desert is the fastest moving desert on Earth; according to some researchers, the Gobi Desert swallows up over 1,300 square miles (3,370km²) of land annually. This has destroyed many villages in its path. Currently, photos show that the Gobi Desert has expanded to the point the entire nation of Croatia (about 4 million[29]) could fit inside its area.[30] This is causing a major problem for the people of China. They will soon have to deal with the desert as it creeps closer. Although the Gobi Desert itself is still a distance away from Beijing, reports from field studies state there are large sand dunes forming only 70km (43.5mi) outside the city.[31]

South America is another area affected by desertification, as 25% of the land is classified as drylands. In Argentina specifically, drylands represent more than half of the total land area, and desertification has the potential to disrupt the nation's food supply.[32]

Mongolia is an area affected by desertification due to overgrazing. In the 1990s after the fall of communism in the country, the people were motivated to become herders. This resulted in the doubling of the number of herders and overgrazing of the Mongolian grasslands. Now 90% of the Mongolian grasslands is fragile dry land.[33] The overpopulation in Mongolia is another cause of the overgrazing with many herders struggling to provide food for their family.[34]

Effects

Sand and dust storms

There has been a 25% increase in global annual dust emissions between the late nineteenth century to present day.[35] The increase of desertification has also increased the amount of loose sand and dust that the wind can pick up ultimately resulting in a storm. For example, dust storms in the Middle East “are becoming more frequent and intense in recent years” because “long-term reductions in rainfall promot[ing] lower soil moisture and vegetative cover”.[36]

Dust storms can contribute to certain respiratory disorders such as pneumonia, skin irritations, asthma and many more.[37] They can pollute open water, reduce the effectiveness of clean energy efforts, and halt most forms of transportation.

Dust and sand storms can have a negative effect on the climate which can make desertification worse. Dust particles in the air scatter incoming radiation from the sun. The dust can provide momentary coverage for the ground temperature but the atmospheric temperature will increase. This can disform and shorten the life time of clouds which can result in less rainfall.[38]

Food security

Global food security is being threatened by desertification and overpopulation. The more the population grows, the more food that has to be grown. The agricultural business is being displaced from one country to another. For example, Europe on average imports over 50% of its food. Meanwhile, 44% of agricultural land is located in dry lands and it supplies 60% of the world's food production. Desertification is decreasing the amount of sustainable land for agricultural uses but demands are continuously growing. In the near future, the demands will overcome the supply.[39]

Vegetation patterning

As the desertification takes place, the landscape may progress through different stages and continuously transform in appearance. On gradually sloped terrain, desertification can create increasingly larger empty spaces over a large strip of land, a phenomenon known as "brousse tigrée". A mathematical model of this phenomenon proposed by C. Klausmeier attributes this patterning to dynamics in plant-water interaction.[40] One outcome of this observation suggests an optimal planting strategy for agriculture in arid environments.[41]

Causes

Preventing man-made overgrazing

Goats inside of a pen in Norte Chico, Chile. Overgrazing of drylands by poorly managed traditional herding is one of the primary causes of desertification.

Wildebeest in Masai Mara during the Great Migration. Overgrazing is not necessarily caused by nomadic grazers in large travelling herd populations.[42][43]

The immediate cause is the loss of most vegetation. This is driven by a number of factors, alone or in combination, such as drought, climatic shifts, tillage for agriculture, overgrazing and deforestation for fuel or construction materials. Vegetation plays a major role in determining the biological composition of the soil. Studies have shown that, in many environments, the rate of erosion and runoff decreases exponentially with increased vegetation cover.[44] Unprotected, dry soil surfaces blow away with the wind or are washed away by flash floods, leaving infertile lower soil layers that bake in the sun and become an unproductive hardpan.

Many scientists think that one of the most common causes is overgrazing, too much consumption of vegetation by cattle or other livestock.

Scientists agree that the existence of a desert in the place where the Sahara desert is now located is due to a natural climate cycle; this cycle often causes a lack of water in the area from time to time. There is a suggestion that the last time that the Sahara was converted from savanna to desert it was partially due to overgrazing by the cattle of the local population.[45]

Researchers from Hacettepe University have reported that Saharan soil may have bio-available iron and also some essential macro and micro nutrient elements suitable for use as fertilizer for growing wheat. It has been shown that Saharan soil may have the potential of producing bioavailable iron when illuminated with visible light and also it has some essential macro and micro nutrient elements. In this study the impact of various growth media on development of some bread wheat (Triticum aestivum L.) and durum wheat (Triticum durum L.) cultivars have been investigated. As a four different nutrient media, Hewitt nutrient solution [1], illuminated and non-illuminated Saharan desert soil solutions and distilled water have been utilized. Shoot length (cm.seedling-1), leaf area (cm2 seedling-1) and photosynthetic pigments [chlorophyll a, chlorophyll b and carotenoids, mg ml-1 g fresh weight (g fw)-1] have been determined. The results of this study indicate that, wheat varieties fed by irradiated Saharan soil solution gave comparable results to Hewitt nutrient solution.[46]

Overpopulation is one of the most dangerous factors contributing to desertification. Human populations are increasing at exponential rates, which leads to overgrazing, over-farming and deforestation, as previously acceptable techniques are becoming less sustainable.[47]

Climate change is likely a major contributing factor in the desertification process, as simulations suggest the greenhouse effect may increase the spread of deserts by as much as 20%.[3]

There are multiple reasons farmers use intensive farming as opposed to extensive farming but the main reason is to maximize yields.[38] By increasing productivity, they require a lot more fertilizer, pesticides, and labor to upkeep machinery. This continuous use of the land rapidly depletes the nutrients of the soil causing desertification to spread.[48][49]

Poverty

At least 90% of the inhabitants of drylands live in developing countries, where they also suffer from poor economic and social conditions.[18] This situation is exacerbated by land degradation because of the reduction in productivity, the precariousness of living conditions and the difficulty of access to resources and opportunities.[50]

A downward spiral is created in many underdeveloped countries by overgrazing, land exhaustion and overdrafting of groundwater in many of the marginally productive world regions due to overpopulation pressures to exploit marginal drylands for farming. Decision-makers are understandably averse to invest in arid zones with low potential. This absence of investment contributes to the marginalisation of these zones. When unfavourable agro-climatic conditions are combined with an absence of infrastructure and access to markets, as well as poorly adapted production techniques and an underfed and undereducated population, most such zones are excluded from development.[51]

Desertification often causes rural lands to become unable to support the same sized populations that previously lived there. This results in mass migrations out of rural areas and into urban areas (urbanisation), particularly in Africa. These migrations into the cities often cause large numbers of unemployed people, who end up living in slums.[52][53]

In Mongolia the land is 90% fragile dry land, which causes many herders to migrate to the city for work. With very limited resources the herders that stay in the dry land graze very carefully in order to preserve the land. With the increasing population of Mongolia it is very difficult to stay a herder for long.[34]

The number of these environmental refugees grows every year, with projections for sub-Saharan Africa showing a probable increase from 14 million in 2010 to nearly 200 million by 2050. This presents a future crisis for the region, as neighboring nations do not always have the ability to support large populations of refugees.[54][55]

Agriculture is a main source of income for many desert communities. The increase in desertification in these regions has degraded the land to such an extent where people can no longer productively farm and make a profit. This has negatively impacted the economy and increased poverty rates.[56]

Countermeasures

Techniques and countermeasures exist for mitigating or reversing the effects of desertification, and some possess varying levels of difficulty. For some, there are numerous barriers to their implementation. Yet for others, the solution simply requires the exercise of human reason.

One proposed barrier is that the costs of adopting sustainable agricultural practices sometimes exceed the benefits for individual farmers, even while they are socially and environmentally beneficial.[58] Another issue is a lack of political will, and lack of funding to support land reclamation and anti-desertification programs.[59]

Reforestation gets at one of the root causes of desertification and is not just a treatment of the symptoms. Environmental organizations[62] work in places where deforestation and desertification are contributing to extreme poverty. There they focus primarily on educating the local population about the dangers of deforestation and sometimes employ them to grow seedlings, which they transfer to severely deforested areas during the rainy season.[63] The Food and Agriculture Organization of the United Nations launched the FAO Drylands Restoration Initiative in 2012 to draw together knowledge and experience on dryland restoration.[64] In 2015, FAO published global guidelines for the restoration of degraded forests and landscapes in drylands, in collaboration with the Turkish Ministry of Forestry and Water Affairs and the Turkish Cooperation and Coordination Agency.[65]

The "Green Wall of China" is a high-profile example of one method that has been finding success in this battle with desertification.[according to whom?]. This wall is a much larger-scale version of what American farmers did in the 1930s to stop the great Midwest dust bowl. This plan was proposed in the late 1970s, and has become a major ecological engineering project that is not predicted to end until the year 2055. According to Chinese reports, there have been nearly 66billion trees planted in China's great green wall.[66] The green wall of China has decreased desert land in China by an annual average of 1,980 square km.[67] The frequency of sandstorms nationwide have fallen 20% due to the green wall.[68] Due to the success that China has been finding in stopping the spread of desertification, plans are currently be made in Africa to start a "wall" along the borders of the Sahara desert as well to be financed by the United Nations Global Environment Facility trust.[69]

in 2007 the African Union started the great green wall of Africa project in order to combat desertification in 20 countries. the wall is 8000km wide stretching across the entire width of the continent and has 8 billion dollars in support of the project. The great green wall of Africa has restored 36 million hectares of land to the countries and has created many job opportunities for those who dwell near it.[70] The great green wall has created over 20,000 jobs in Nigeria alone.[71]

Some soils (for example, clay), due to lack of water can become consolidated rather than porous (as in the case of sandy soils). Some techniques as zaï or tillage are then used to still allow the planting of crops.[72] Waffle gardens can also help as they can provide protection of the plants against wind/sandblasting, and increase the hours of shade falling on the plant.[73]

Another technique that is useful is contour trenching. This involves the digging of 150m long, 1m deep trenches in the soil. The trenches are made parallel to the height lines of the landscape, preventing the water from flowing within the trenches and causing erosion. Stone walls are placed around the trenches to prevent the trenches from closing up again. The method was invented by Peter Westerveld.[74]

Another way to restore soil fertility is through the use of nitrogen-rich fertilizer. Due to the higher cost of this fertilizer, many smallholder farmers are reluctant to use it, especially in areas where subsistence farming is common.[77] Several nations, including India, Zambia, and Malawi have responded to this by implementing subsidies to help encourage adoption of this technique.[78]

Some research centres (such as Bel-Air Research Center IRD/ISRA/UCAD) are also experimenting with the inoculation of tree species with mycorrhiza in arid zones. The mycorrhiza are basically fungi attaching themselves to the roots of the plants. They hereby create a symbiotic relation with the trees, increasing the surface area of the tree's roots greatly (allowing the tree to gather much more nutrient from the soil).[79]

As there are many different types of deserts, there are also different types of desert reclamation methodologies. An example for this is the salt flats in the Rub' al Khali desert in Saudi Arabia. These salt flats are one of the most promising desert areas for seawater agriculture and could be revitalized without the use of freshwater or much energy.[80]

Farmer-managed natural regeneration (FMNR) is another technique that has produced successful results for desert reclamation. Since 1980, this method to reforest degraded landscape has been applied with some success in Niger. This simple and low-cost method has enabled farmers to regenerate some 30,000 square kilometers in Niger. The process involves enabling native sprouting tree growth through selective pruning of shrub shoots. The residue from pruned trees can be used to provide mulching for fields thus increasing soil water retention and reducing evaporation. Additionally, properly spaced and pruned trees can increase crop yields. The Humbo Assisted Regeneration Project which uses FMNR techniques in Ethiopia has received money from The World Bank's BioCarbon Fund, which supports projects that sequester or conserve carbon in forests or agricultural ecosystems.[81]

Managed grazing

Restoring grasslands store CO2 from the air as plant material. Grazing livestock, usually not left to wander, would eat the grass and would minimize any grass growth while grass left alone would eventually grow to cover its own growing buds, preventing them from photosynthesizing and killing the plant.[82] A method proposed to restore grasslands uses fences with many small paddocks and moving herds from one paddock to another after a day or two in order to mimic natural grazers and allowing the grass to grow optimally.[82][83][84] It is estimated that increasing the carbon content of the soils in the world's 3.5 billion hectares of agricultural grassland would offset nearly 12 years of CO2 emissions.[82]

Related Research Articles

Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, game reserves, or nature reserves. It can also be caused by immobile, travel restricted populations of native or non-native wild animals. However, "overgrazing" is a controversial concept, based on equilibrium system theory. A strong indicator of overgrazing is where additional feed needs to be brought in from outside the farm, often to support livestock through the winter. Traditionally this feed was sourced on the farm, with fewer animals being kept and some fields being used for hay and silage production. Modern farm businesses often choose to keep more animals than their land can support alone; buying in external feed to offset this.

The Sahara desert, as defined by the World Wide Fund for Nature (WWF), includes the hyper-arid center of the Sahara, between latitudes 18° N and 30° N. It is one of several desert and xeric shrubland ecoregions that cover the northern portion of the African continent.

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Mauritania, a country in the western region of the continent of Africa, is generally flat, its 1,030,700 square kilometres forming vast, arid plains broken by occasional ridges and clifflike outcroppings. It borders the North Atlantic Ocean, between Senegal and Western Sahara, Mali and Algeria. It is considered part of both the Sahel and the Maghreb. A series of scarps face southwest, longitudinally bisecting these plains in the center of the country. The scarps also separate a series of sandstone plateaus, the highest of which is the Adrar Plateau, reaching an elevation of 500 metres. Spring-fed oases lie at the foot of some of the scarps. Isolated peaks, often rich in minerals, rise above the plateaus; the smaller peaks are called guelbs and the larger ones kedias. The concentric Guelb er Richat is a prominent feature of the north-central region. Kediet ej Jill, near the city of Zouîrât, has an elevation of 1,000 metres and is the highest peak.

A dust storm, also called sandstorm, is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Fine particles are transported by saltation and suspension, a process that moves soil from one place and deposits it in another.

The Sahel is the ecoclimatic and biogeographic zone of transition in Africa between the Sahara to the north and the Sudanian Savanna to the south. Having a semi-arid climate, it stretches across the south-central latitudes of Northern Africa between the Atlantic Ocean and the Red Sea. The name is derived from the Arabic term for "coast, shore": this is explained as being used in a figurative sense. However, such figurative use is unattested in Classical Arabic, and it has been suggested that the word may originally have been derived from the Arabic word sahl سهل "plain" instead.

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Desert greening is the process of man-made reclamation of deserts for ecological reasons (biodiversity), farming and forestry, but also for reclamation of natural water systems and other ecological systems that support life. The term "desert greening" is intended to apply to both cold and hot arid and semi-arid deserts. It does not apply to ice capped or permafrost regions. Desert greening has the potential to help solve global water, energy, and food crises. It pertains to roughly 32 million square kilometres of land.

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↑ Rafferty, John P.; Pimm, Stuart L. (2019). "Desertification". Encyclopædia Britannica. Retrieved 2019-11-06. the process by which natural or human causes reduce the biological productivity of drylands (arid and semiarid lands). ... The concept does not refer to the physical expansion of existing deserts but rather to the various processes that threaten all dryland ecosystems.

↑ Rafferty, John P.; Pimm, Stuart L. (2019). "Desertification". Encyclopædia Britannica. Retrieved 2019-11-06. The concept does not refer to the physical expansion of existing deserts but rather to the various processes that threaten all dryland ecosystems.

↑ Gillet, Kit (4/1/2011). "A way of life in crisis: on the sparsely inhabited steppes of Mongolia, the lifestyle of the nomadic herder has always been a hard one. But as livestock die in their millions during the increasingly frequent bitter winters, and pasturelands disappear due to overgrazing and desertification, this traditional culture is struggling to survive". Circle Publishing Ltd.Check date values in: |date= (help)

1 2 Gillet, Kit (April 2011). "A way of life in crisis: on the sparsely inhabited steppes of Mongolia, the lifestyle of the nomadic herder has always been a hard one. But as livestock die in their millions during the increasingly frequent bitter winters, and pasturelands disappear due to overgrazing and desertification, this traditional culture is struggling to survive". Circle Publishing Ltd.

↑ Gadzama, Njidda Mamadu (2017). "Attenuation of the effects of desertification through sustainable development of Great Green Wall in the Sahel of Africa". World Journal of Science, Technology and Sustainable Development. 14 (4): 279–289. doi:10.1108/WJSTSD-02-2016-0021.

↑ Gadzama, Njidda (2017). "Attenuation of the Effects of Desertification through Sustainable Development of Great Green Wall in the Sahel of Africa". World Journal of Science, Technology and Sustainable Development. 14 (4): 279–289. doi:10.1108/WJSTSD-02-2016-0021.

Holtz, Uwe (2007). Implementing the United Nations Convention to Combat Desertification from a parliamentary point of view – Critical assessment and challenges ahead. Online at

Holtz, Uwe (2013). Role of parliamentarians in the implementation process of the UN Convention to Combat Desertification. A guide to Parliamentary Action, ed. Secretariat of the UNCCD, Bonn ISBN978-92-95043-69-5. Online at